The present invention relates to the field of audio signal processing to improve the perception upon playing back.
International patent application WO2012088336 is known for example, which describes a method of processing an audio sound source to create four-dimensional spatialized sound.
A virtual sound source can be moved along a path in a three-dimensional space over a specified period of time to obtain the location of the four-dimensional sound.
The various embodiments described herein provide methods and systems for converting existing mono, 2-channel and/or multi-channel audio signals into spatialized audio signals having two or more audio channels.
The various embodiments also describe the methods, systems and apparatus for generating low-frequency effects, and center channel signals from incoming audio signals having one or more channels.
A device is known from the patent application WO9914983, which makes it possible to create and use a pair of opposing loudspeakers of headphones, with the sensation of a sound source being moved away from the area between said loudspeakers. The device comprises:                a series of audio inputs representing audio signals projected from a theoretical sound source located remotely from the theoretical listener;        a first mixing matrix, connected to the audio inputs and a series of feedback inputs, which produces a predetermined combination of said audio inputs composing intermediate output signals;        a filter system, which filters said intermediate output signals and generates filtered intermediate output signals and the series of feedback inputs, and which comprises separate filters for filtering the direct response and the fast response and an approximation of the reverberated response, and for filtering the feedback response so as to generate the feedback inputs; and        a second mixing matrix, which combines the filtered intermediate output signals so as to produce right channel and left channel stereo outputs.        
European Patent EP2119306 describes a device for processing an audio sound source to create four-dimensional spatialized sound. A virtual sound source can be moved along a path in a three-dimensional space over a specified period of time to obtain the location of the four-dimensional sound.
A binaural filter for a desired space point is applied to the audio waveform to produce a spatialized waveform so that, when the spatialized waveform is played from a pair of loudspeakers, the sound seems to come from the selected space point instead of the loudspeakers.
A binaural filter for a space point is simulated by interpolation of the nearest one of the binaural filters selected from a plurality of predefined binaural filters.
The audio waveform can be digitally processed by overlapping data blocks using a Fourier transform short time.
The located sound can be subsequently processed for chamber and Doppler shift simulation.
The present invention relates to a method for processing an original audio signal having N.x channels, with N being greater than 1 and x being greater than or equal to 0, comprising a step of multi-channel processing said input audio signal using a multichannel convolution with a predefined footprint, said footprint being developed by the capture of a reference sound by a loudspeaker system placed in a reference space characterized in that it comprises an additional step of selecting at least one footprint of a plurality of footprints previously developed in different sound environments.
The patent application WO2012172264 discloses a method for processing an original audio signal having N.x channels, with N being greater than 1 and x being greater than or equal to 0, comprising a step of multi-channel processing said input audio signal by a multichannel convolution with a predetermined footprint, with said footprint being developed by the capture of a reference sound by a loudspeaker system placed in a reference space characterized in that it comprises an additional step of selecting at least one footprint of a plurality of footprints previously developed in different sound environments.
The patent application WO9725834 provides another method and device for processing multichannel audio signals, with each channel corresponding to a loudspeaker placed at a particular point of a room so as to give, via headphones, the impression that multiple “ghost” loudspeakers are distributed over the room. HRTF (Head Related Transfer Functions) transfer functions are selected with respect to the head while taking into account the height and azimuth of each considered loudspeaker with respect to the listener. Each channel is subject to HRTF filtering so that, when such channels are combined into the left and right channels and output by headphones, the listener has the impression that the sound actually comes from the ghost loudspeakers distributed in the virtual room. Sets of HRTF coefficients entered into databases from a large number of individuals and the use, for the concerned listener, of an optimal HRTF set provides him/her with listening impressions similar to the one which an isolated listener would have if listening to multiple loudspeakers distributed throughout the volume of a room. The application of an HRTF function at the output of left and right channels makes it possible, when listening with headphones, to give the impression of listening without headphones.
Prior art solutions are limited by the intrinsic qualities of playback means (headphones or loudspeakers) and the suitability thereof for the processing applied to the audio signal.
In addition, some processing of the prior art require significant computing power, incompatible with the capabilities of tablets, phones or portable players.